Prostate cancer is a common occurrence in the aging population, with one in ten men destined to develop the disease. 40% of patients with prostate cancer experience a recurrence after definitive treatment. This study addresses the as-yet unresolved problem of the optimal management of early recurrence as manifested by increase in the accepted marker for this disease, PSA. Vitamin D, an agent with cell-differentiating properties, has been shown to inhibit angiogenesis and cause differentiation of prostate cancer cells in the laboratory and to affect PSA favorably in clinical studies of patients with advanced prostate cancer. This study will assess the effects of vitamin D in patients with sub-clinical biochemical relapses of prostate cancer as indicated by rising PSA but low tumor burdens, with the potential for developing an approach to this problem that will delay or prevent progression.